Hearing aids typically use a microphone and an amplifier to receive and amplify sound. But this arrangement can result in feedback when a telephone earpiece is placed up to the wearer's ear. Thus, hearing aids frequently come with an alternate input device referred to as a “telecoil” and a means to switch the hearing aid from a microphone mode to a telecoil mode, or a combination microphone/telecoil mode.
A hearing aid telecoil is an induction coil that typically consists of a rod encircled by turns of a copper wire. When placed in a varying magnetic field, an alternating current is induced in the wire so that the telecoil may receive the electrical audio signal from an inductive field emitted from a HACD, such as a telephone. Thus, a user can pick up the sound by coupling the telecoil to an inductive field, thereby bypassing background noise and preventing feedback associated with a sound wave signal.
Unfortunately, a telecoil may also pick up unwanted electromagnetic interference (EMI) from a variety of sources, such as power transformers, fluorescent lighting, trains and digital wireless telephones. Interference from digital wireless phones is of particular concern given the explosion in the use of such devices and the variety of EMI associated with their use, such as that caused by radio frequency (RF) emissions, display backlighting, display strobing, and processor noise.
The strength of the electrical current induced in a hearing aid telecoil is dependent on the strength of the magnetic field and the relative position of the telecoil with respect to the inductive field generated by the HACD. Maximum inductive coupling is created when the electromagnetic field created by the HACD is parallel to the hearing aid telecoil and minimum inductive coupling occurs when the electromagnetic field is orthogonal to the telecoil. Thus, it is desirable to orient the inductive field parallel to the telecoil when coupling a hearing aid and HACD.
Because it is often difficult for a hearing aid user to obtain the proper relative positioning between the HACD and the hearing aid telecoil, users are often compelled to reorient the HACD in an effort to find a “hot spot” where the inductive field of the HACD is relatively parallel to the telecoil. This often results in a position of the device that is not only uncomfortable but not optimal for the device operation.
Further complicating the matter is that during the hearing aid manufacturing process, the telecoil is subject to reorientation or shifting. For example, in-the-canal (ITC) and completely-in-the-canal (CIC) hearing aids are manufactured using techniques that allow most or all of the hearing aid electronics to be molded into a unit that fits into the ear canal, whereby the telecoil can wind up in virtually any position. Thus, the telecoil orientation may be different even between two hearing aids that are produced by the same manufacturer.
Thus, there is a need for a system and method for optimizing the inductive coupling between an HACD and a telecoil of a hearing aid worn by a user without the user having to reorient the HACD.